As the digitalization technology has made rapid progress, image forming technologies by an electrophotographic method for copiers, printers, and the like have come into wide use and the number of such devices in use has increased greatly.
Generally, the recent electrophotographic technology has made vigorous researches and developments aiming the four points below.
(1) Downsizing the image forming device
(2) Speeding up the processing of the image forming device
(3) Forming high-quality color images
(4) Reducing the image forming power (for power saving)
To accomplish the purposes (1) to (3), you must rotate developing rollers of small diameters at a high speed. However, this method may contaminate images with scattered toner and deteriorate the developing rollers by toners fused thereto. These problems are hard to be solved.
A technology has been disclosed to solve such problems. This technology uses toner particles of equal electrostatic properties to increase the charging speed and the charge retaining ability of toner particles. (For example, see Patent Document 1)
As for power saving of (4), it is inevitable to reduce the flat power rate and power cost because, as a trend of the times, network environments have been arranged more conveniently, printers have been used more frequently in offices, and the digital equipment such as printers and facsimile equipment has been widely used in home.
Further, the electrophotographic image forming technology is expected to fan out into the print-on-demand (POD) and book-on-demand (BOD) fields in which the required number of copies can be made only on demand without preparing any plate.
However, the current image forming technology excels in processing speed but only the limited kinds of paper are available to the technology. For example, when processed by the technology, thin paper may have wrinkles on it and general coated glossy paper may have blisters (which cause image defects) due to steam on it. Further it has been difficult to give color reproducibility to form beautiful color images without being affected by collation accuracies (in book binding) and paper kinds.
To solve these problems, various tries have been made. One of the tries is to use chemical toners such as a representative polymeric toner which was described in above Patent Document 1. The try dynamically controls the structure of toner particles to design toner to solve the above problems. For example, a toner technology modifies the surfaces of toner particles by fusing resin particles to surfaces of another kind of resin particles which contains resins and colorants. This technology can suppress colorants from appearing on the surfaces of toner particles and form images which are stable in high humidity environments. Another toner technology controls dispersion and occupation of toner-containing components in toner production processes to make toner particles hard to be affected by environmental factors such as temperature and humidity. However, these technologies are not satisfactory yet. (For example, see Patent Document 2, Patent Document 3, and Patent Document 4.)
Particularly, this technology which improves toner performance by coating toner particle surfaces with resin has been proposed long before, but the resin particles may be coagulated during storage and transportation and cannot fully keep the stability in the charging speed and charge retention.
Patent Document 1: Japanese Non-Examined Patent Publication No. 2004-54240
Patent Document 2: Japanese Non-Examined Patent Publication No. 2002-116574
Patent Document 3: Japanese Non-Examined Patent Publication No. 2002-351142
Patent Document 4: Japanese Non-Examined Patent Publication No. H10-26842
In view of the foregoing, it is a main object of this invention to provide new toners for electrophotographic image forming apparatus such as small and fast copiers, printers, and facsimile equipment and more particularly to provide toners.
Still, another object of this invention is to provide toners which have greatly improved the charging speed and charge retaining ability, can form stable toner images even when the developing unit is downsized, can fix toner images to transferring materials at lower temperatures, and will not be coagulated together without being cooled or heat-insulated during storage or transportation.
Another object of this invention is to provide toners which have a sufficient fixing strength even at a low fixing temperature and can form even, excellent, uniform, and glossy images.
Further, this invention can provide toners which can form stable images on such kinds of paper (such as coated glossy paper and cardboard) that are hard to receive images by conventional technologies. In other words, still another object of this invention is to provide toners which enable selection of more kinds of paper for formation of toner images and fan-out of the on-demand image forming technology which can make the required number of copies without preparing any plate.